Study On The Determination Of Antioxidant Capacity And Resource Screening In Stevia Rebaudiana

Stevia, as being natural sweeter and additive, has been applied on process of drinks, foods and feed. In recently years, the study of stevia were mainly concentrated in the extraction and application of stevia sugar glucoside at home and abroad. But at the same time in the leaf of stevia also contains flavonoids, phenolic compounds, amino acids, lipids, naphtha and trace elements, etc. Those constitutes have antioxidant activity. So the purpose of this study was to analyze the content of flavonoids, phenolic compounds and DPPH free radicals clearance rate. At the same time screened germplasm resources, to lay the foundation for breeding new varieties with high oxidation of stevia.The quantitative determination of flavonoids using NaNO2-Al(NO3)3colorimetric method. By optimizing the processing, taken0.1g stevia samples, absorbed axtract1.0mL were more suitable for reaction and colorimetry. It’s RSD1.08%; The quantitative determination of phenolic compounds used Folin-Ciocalteu colorimetric method. After optimization we found that when the volume rotio of1.5mL lmol/L Folin-Ciocalteuand3.0mL12%Na2CO3was1:2, the result of the method was the best. The determination of antioxidant activity used DPPH free radicals clearance rate method. The numbers of clearance rate on the behalf of the antioxidant activity. It’s RSD is0.91%. Those results showed that the colorimetry have high accuracy, reproducibility and good linear relationship. And as the colormetry has many advantages, such as simple operation, low equipment requirement, so it is suitable for the determination in stevia leaf of flavonoids and polyphenols content and DPPH free radicals clearance rate. It can provide a certain basis for the research of stevia antioxidant aspects of the development and utilization.In the practical breeding, we often need choose some better varieties from large quantities of materials. And near infrared spectrum technology has many advantages, for example, fast, high efficiency, no pollution, no loss, etc. So569stevia leaf samples were scanned by NIRSystem and307representive samples were selected and analyzed their flavonoids, phenolic compounds and DPPH free radicals clearance rate by the suitable colorimetric method, then use the data to develop calibrations. Results showed that compared with other mathematical treatments, the model developed with mathematical treatment "1,4,4,1" had the best result in calibrating the contents of flavonoids and phenolic compounds. In the scattering process, for flavonoids, the results of treatments were over fitting, their effects were rather than the contrast. But for phenolic compounds, SNV and SMSC with mathematical treatment "1,4,4,1", the1-VR were0.947, and RPD were4.342and4.336. However, on the whole the effect of5kinds of treatment methods were worse than the contrast. So choose the contrast to develop calibration model for and phenolic compounds was oppropriate. In comparing of the regression method, for flavonoids, the effect of PLS was the best, the minimum value of SECV was30.696, the maximum value of1-VR was0.788, the external inspection also well. For phenolic compounds, the effect of MPLS was the best, the minimum value of SECV was2.936, the maximum value of1-VR wasO.942. But for DPPH free radicals clearance rate, the1-VR of five treatment methods and contrast were all at around0.2, all less than1. So it can say the NIRS calibration model for DPPH free radicals clearance rate was not ideal.Use the NIRS model to screened1032stevia samples, predicted their contents of flavonoids and phenolic compounds, the predictive value of flavonoids and phenolic compounds ranges respectively were130.156-435.731mg/g and28.960-95.170mg/g. Then screened27stevia samples that have high contents of flavonoids and phenolic compounds, it provide certain basis for screen stevia samples which has high flavonoids and phenolic compounds.